The present invention relates to the art of rock boring and more particularly to a rotary bit which comprises three toothed conical rotary elements on which are disposed hard metal tips. The tips may be inserts. Such bits are typically rotated under the weight of a drill collar and drill pipe. This weight forces the bits into the rock or other ground formations and the rotation causes the rotatably mounted cones to rotate about their own axes. The teeth or tips chip and crush the rock or other formations.
While particularly adapted for drilling oil wells, it will be understood that it also has application for other ground boring requirements.
The prior art drill bit assemblies have usually been constructed with channels or other non-cutting areas between rings of teeth. These areas have been provided, in the prior art devices, for the purpose of providing cleaning clearance for the cutting teeth. The present inventor has found that this theory and construction are based on an incorrect theoretical basis. More particularly, such cleaning clearances result in recompressing material which has been cut off and chewed up by adjacent teeth or rows of teeth. The practical effect of the use of such grooves is to substantially reduce the number of cutting teeth which may be disposed on a given size cone, thus reducing rates of penetration in drilling operations.
The prior art drill bit also typically has teeth which have elongated cutting edges which are disposed in generally parallel relationship to the axis of rotation of the cone. A difficulty with these prior art drill bits, is that the resultant force on the cone is inclined substantially from the axis of rotation. This results in a spiralling action of the drill bit, as it drills down into the ground.
Various drill bit constructions, such as those shown in U.S. Pat. Nos. 3,385,385, 4,187,922, and 2,990,025, have not proven wholly satisfactory.
It is an object of the invention to provide apparatus which will provide more rapid drilling and improved penetration rates, even when drilling relatively hard rock.
An object of the invention is to provide apparatus which will inherently tend to move in a more rectilinear path as it passes down into the ground, and which tends to avoid the spiralling action of the prior art drill bits, while accomplishing the other objects of the invention.
An object of the invention is to provide apparatus which distribute the wear of the cutting teeth over substantially all the cutting teeth of each cone so that the life of the cone is maximized.
Another object of the present invention is to provide drill bit apparatus which will provide improved durability and longer service life.
Another object of the invention is to provide a construction which reduces overloading, shock loads and load variations imposed on the cone bearings so that the bearing life will be substantially increased over the prior art construction.